The present invention relates to a heat resistant, electroconductive silicone elastomer composition. More particularly, the invention relates to a heat resistant, electroconductive silicone elastomer composition having reduced thermal oxidation caused generally when a metal powder is added to a silicone elastomer used as an electric contact material to reduce its resistivity.
An electroconductive silicone elastomer composition obtained by blending carbon powder to a silicone elastomer composition has been used as an electric contact material or electromagnetic wave shielding material.
Though the electroconductive silicone elastomer composition containing carbon powder is relatively stable thermally, its volume resistivity could not be reduced to lower than 1.OMEGA..cm and, therefore, it could not be used when a lower volume resistivity was required. Various processes have been proposed for obtaining an electroconductive silicone elastomer composition having a volume resistivity of 1.times.10.sup.-2 to 10.sup.-3 .OMEGA..cm by mixing a silicone elastomer with various metal powders.
However, in these processes wherein the metal powder is used, the metal powder must be incorporated in the silicone elastomer in a large amount for obtaining an intended resistivity. Consequently, the physical properties of the silicone elastomer are damaged seriously. Another defect of these processes is that when the silicone elastomer composition is exposed to a high temperature, its resistivity is changed with time, since the resistivity is increased by the oxidation of the metal powder.
A method for overcoming these defects has been disclosed in the specification of Japanese Patent Publication No. 6223/1975 wherein an amine-containing or phosphorous-containing antioxidant is used. However, this method is ineffective for inhibiting the thermal oxidation at such a high temperature as employed when the silicone elastomer is used.
After intensive investigations made for the purpose of overcoming the defects of the prior art, the present inventors have found that an electroconductive silicone elastomer composition having a low resistivity, which is substantially unchanged with time even at a high temperature, and excellent moisture resistance, can be obtained by adding nickel-coated carbon to a silicone elastomer composition. The present application is based on this finding.